This application claims priority to prior applications JP 2002-70354 and JP 2002-148345, the disclosures of which are incorporated herein by reference.
The present invention relates to a glass preform as a raw material for producing an optical waveguide material, such as a photonic crystal fiber (PCF), a holeyfiber, or a photonic bandgap fiber (PBF), having a number of air holes periodically arranged in its cross section (having a periodic structure in its cross section) and to a method of producing the glass preform.
An optical waveguide material, such as a photonic crystal fiber, a holey fiber, or a photonic bandgap fiber, having a periodic structure in its cross section is excellent in optical transmission characteristic and therefore attracts attention as an important material in a future optical communication system. In order to produce the above-mentioned optical waveguide material, proposal has been made of a first method of drawing a bundle of circular cylindrical silica glass capillaries to obtain an integral structure and a second method of preparing a bundle of polygonal columnar silica glass capillaries as a preform and drawing the preform to obtain an integral structure.
In the first method, however, it is difficult to precisely arrange the capillaries in a regular periodic structure. Therefore, it is difficult to obtain an optical waveguide material having a periodic structure. In addition, a number of air gaps are present between the capillaries. Therefore, the optical waveguide material inevitably has interstitial sites between the air holes. In the second method, it is easy to regularly arrange the capillaries. However, in order to process the capillaries into a polygonal shape in section, much labor is required and, therefore, production cost is increased. If the processing accuracy is insufficient, the optical waveguide material inevitably has interstitial sites.